Conventionally, there is known a data distribution system in which a distribution device holds a data file of various contents, such as sound, motion picture, and so forth, as a distribution object, and each data file is distributed to a client user terminal in response to a request therefrom. In recent years, peer-to-peer type data exchange systems for exchanging a data file directly between user terminals (peers) have become available. In some of such data exchange systems, a data file is divided into a plurality of file pieces and each file piece is exchanged. According to such a technique, each user terminal can obtain from different devices a plurality of file pieces constituting a data file which the user wishes to obtain. This makes it possible to exchange large volume data among user terminals, while avoiding concentration of network traffic to a specific distribution device or a specific user terminal.